What defines adulthood in 2021? Culturally, it’s not always clear—certainly not when the most popular movies in the world are about comic book heroes or a hostile housing market and poor employment options conspire to leave children living at home long after college. Scientifically, we know now that the human brain continues to develop well into the mid-twenties, explaining a lot of our rash decisions in college as the work of a still-inchoate brain. In the eyes of the law, however, the definition of adulthood is more cut-and-dried: children reach the age of majority on their 18th birthdays.When a child’s parents are divorced, this overnight transition has major ramifications for family structure and responsibilities. The lifting of guidelines and the sudden independence is often not a relief but an unmooring, especially for kids caught between households and parental tensions. Here’s what you should understand about divorce after a child turns 18.When parents divorce, children have little say in the matter of who goes where and when. While some states allow teenage children to make suggestions, the decision ultimately lies with the expertise of a family court judge. Once a child reaches age 18, however, any arrangements regarding primary custody or visitation rights expire, and these young adults can decide for themselves where to live—whether that’s with the parent who had primary custody, the other parent, or neither. This decision is not easy for most children to make.Just as custody and visitation rights expire, court-ordered child support ends at the 18th birthday as well. While this can be a relief for a parent who has felt burdened by child support payments, it can leave the other parent feeling as if the bottom has dropped out. With many young people entering college at age 18, good financial planning is important to account for this change.In certain cases, understanding divorce after a child turns 18 is not as self-evident as it usually is. When a child has special needs or a disability that requires legal guardianship, turning 18 years old is not an immediate entry into adulthood. In instances where a child’s future as an adult is an issue that parents will have to consider, a divorce agreement should clear up these considerations, such as voluntary child support after the child’s 18th birthday. Sitting down with an Illinois family law attorney will help you plan a future for a child who may not necessarily be able to navigate adulthood without additional guidance.